peak torque?

I am putting taller tires (205/70R15) on my '03 Jetta and also want to put in a taller 5th gear (.681 or possibly .658) the combination will lower 55 mph rpm to about 1700. I would like to lower the point of peak torque to around 1700 rpm. Anyone know of any modifications to accomplish this? Also anyone that has put the taller gears in want to share their experience with mpg gains and drive ability after the gear change?

Thanks

Mike V said:

I am putting taller tires (205/70R15) on my '03 Jetta and also want to put in a taller 5th gear (.681 or possibly .658) the combination will lower 55 mph rpm to about 1700. I would like to lower the point of peak torque to around 1700 rpm. Anyone know of any modifications to accomplish this? Also anyone that has put the taller gears in want to share their experience with mpg gains and drive ability after the gear change?

Thanks

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Mike, I understand putting taller tires on and going to a longer 5th gear. I have been there, done that.
I am running 195/65x15 tires in place of 195/60x 14 (note 15 inch wheels vs 14 inch wheels). I am also running a EuroTuning 6 speed conversion that adds a 6th gear to my stock 5 speed. Lastly, my transmission has a 3.157 final drive, while your transmission has something like a 3.39 final drive.
I am actually running about 1900 rpm at 70/72 mph in 6th gear.

You do not want to lower the rpm for peak torque. What you want is more torque at 1700 than you have now.

For that you need larger nozzles and a tune. Take a look at my signature, you will see I am up 50% in low end torque compared to stock. All I did was install larger nozzles and get a tune. With that I can pull the bigger tires and the .59 6th gear and still climb any grade on the interstate highway system. Last Sunday, I had no problems sustaining 70 mph going from Sacramento to Reno, over the 7250 ft. Donner Pass.

Depending on how much you want to spend, there's a few options

1) Leave the power stock - I drove a 0.681 5th gear with stock power for a few years and the only time power was ever an issue was when I had a 1500lb trailer behind me trying to do 55 MPH. At 60 or 70 MPH it was fine, below 50 or so it was in 4th.

2) Tune only from any one of the reputable tuners if you would like a bit more pep. This will really transform the car and make it accelerate like before you went taller tires and taller 5th gear. I've had tunes from most of the major tuners here and would recommend Rocketchip "euro" tune for the best low end response though many of the other tuners may have improved things in the years since I've run their tunes.

3) Tune and nozzles - this requires a clutch as well so it gets a lot more expensive.

Don't expect much MPG gain from #1 and 5th gear passing ability will be slightly reduced.

#2 will usually provide a few MPG's and drive better than stock all around

#3 is just more of #2 - probably no more MPG's (depending on how you drive), more power, more $$, etc

#3 along with low viscosity engine and transmission oil netted me my best MPG's by far (mid-upper 50's easily, 60's by driving the speed limit).

None of the above will pay for themselves in MPG's/fuel savings/etc - do them because you want to.